Exhaust control system for dryer hood



K. H. JON ES May 13, 1969 EXHAUST CONTROL SYSTEMFOR DRYER HOOD,

Sheet 1 of 2 Filed April 29. 1966 INVENTOR KenneT/I 14 Tones ATTORNEYS May 13, 1969 K. H. JONES EXHAUST CONTROL SYSTEM FOR DRYER HOOD Sh eet Filed A ril 29, 1966 ATTORNEYS MKM United States Patent 3,443,325 EXHAUST CONTROL SYSTEM FOR DRYER HOOD Kenneth H. Jones, Ramsey, N.J., assiguor to AER Corporation, Ramsey, N.J., a corporation of New Jersey Filed Apr. 29, 1%6, Ser. No. 546,284 Int. Cl. F26b 13/08 US. Cl. 34-114 12 Claims ABSTRACT OF THE DISCLOSURE An exhaust control system for the dryer hood of a paper machine dryer section in which frames support drying cylinders in a drying space above the mill floor to form spaces between the frames and the front and rear walls of the hood. Bafiles located in the spaces between the hood walls and the frames inhibit flow of drying air supplied from below the floor transversely of the drying space to direct the air to a plenum chamber at the top of the hood from which the air and moisture is permitted to escape through an elongated narrow opening at the peak of the plenum chamber.

My invention relates to an exhaust control system for a dryer hood and more particularly to an improved dryer system for a paper making machine which ensures even drying of the paper web across its width.

One of the most difficult problems involved in the manufacture of paper and board is drying of the web after formation thereof. It has been established that the web cannot be dried to the final desired degree in a commercially practicable way except by evaporation of moisture from the paper. As a result paper making machines almost universally include a dryer section comprising a plurality of dryer rolls which are heated by steam or the like fed to the interior of the rolls. These dryer sections also include felts which are brought into intimate contact with the web as it passes around the dryer rolls to assist in removing moisture therefrom. In the course of passage of the web and of the felt through the dryer and around the various rolls, there are formed relatively enclosed spaces in which moisture tends to collect. It will readily be appreciated that if the drying operation is to be effectively achieved, some means must be provided for removing the moisture-laden air from the dryer section.

In the prior art in order to remove moisture from the dryer, the section is covered by a hood and air is supplied from below the section. The air moves up through the dryer section carrying moisture and is removed at the top of the hood generally through an exhaust opening at the rear of the hood.

The hoods employed to cover dryer sections may be of the closed type which are provided with access doors which substantially, completely enclose the section or they may be of the open type wherein no such doors are provided. In both types of hoods there are spaces between the rear roll support frame and the rear wall of the hood and between the front roll support frame and the front of the hood. It will readily be appreciated that there exists in these spaces a stack effect by virtue of which air tends to fiow up these spaces rather than through the space occupied by the web and by the felts. In modern installations the space between the rear roll support frame and the rear wall of the hood is occupied by gearing and steam lines and the like so that access may more readily be had from the front of the dryer to repair breaks and the like. Owing to this fact that the space at the rear is to a large extent occupied, the air supply tends to migrate from the rear to the front of the dryer across the Width of the web as it travels upwardly through the dryer section toward the chamber at the top of the dryer from which it Patented May 13, 1969 is removed. Stated otherwise, the stack effect generally is greater at the front of the dryer than at the rear.

Owing to the construction of hoods of the prior art and for the reasons set forth hereinabove, it has been substantially impossible in the prior art to obtain even removal of drying air from the front, rear and middle of the dryer section. It will be obvious that the uneven removal of drying air results in uneven drying of the web across its width. Moreover, this condition appears to be aggravated as the width of the web increases.

I have invented an exhaust control system for ensuring even drying of a paper web across the width thereof. My arrangement overcomes the disadvantage of the greater stack effect at the front of the dryer hood. My system permits even removal of drying air across the width of a paper web while permitting access to the Web and to the operating parts of the machine as required. My system is extremely simple and is inexpensive for the result achieved thereby.

One object of my invention is to provide an exhaust control system for a paper machine dryer which promotes even drying across the width of the web being dried.

Another object of my invention is to provide a control system for a paper machine dryer which ensures even removal of drying air across the width of the hood while permitting access to the web and to the parts of the dryer as required.

A further object of my invention is to provide an exhaust control system for a dryer hood which overcomes disadvantages resulting from the greater stack effect at the front of the hood.

Still another object of my invention is to provide an exhaust control system for a dryer hood which is simple and economical for the result achieved thereby.

Other and further objects of my invention will appear from the following description.

In general my invention contemplates the provision of an airflow control system for a paper machine dryer section in which I provide within the hood and over the rolls a plenum chamber having top walls sloping from a narrow peak opening toward the front and back walls of the hood and having'curtains for controlling the flow of air upwardly through the respective spaces between the hood front wall and the dryer front frame and between the hood rear wall and dryer rear frame thus to inhibit the migration of drying air from back to front of the hood as it moves up through the dryer. Preferably I control flow through the narrow peak opening to the outlet and permit a controlled flow to the exhaust from the spaces between the front and rear roll support frames and the front and rear walls of the hood. My curtains are readily movable to positions at which access can be had to the interior of the dryer.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIGURE 1 is a partially schematic sectional view of one form of my exhaust control system for a paper machine dryer.

FIGURE 2 is a fragmentary front elevation of a paper machine dryer provided with my exhaust control system with parts broken away.

FIGURE 3 is a fragmentary sectional view of an alternate form of my exhaust control system for a paper machine dryer.

Referring now to the drawings, the dryer section indicated generally by the reference character 10 of a paper making machine includes a plurality of dryer rolls such, for example, as upper dryer rolls 12 and lower dryer rolls 14, as Well as upper felt rolls 16 and lower felt rolls 18. A front frame 20 and a rear frame 22 3 support the rolls 12, 14, 16 and 18 in a manner known to the art.

In the form of paper machines shown in the drawings, drying air is supplied by a duct 24 located in the basement, indicated generally by the reference character 26, below the floor 28 to a distributor 30. The system includes a hood having a top 32, a front wall 34 and a rear wall 36. Air supplied by the distributor 30 is intended to flow upwardly toward the roof 32 and to carry moisture upwardly therewith, ultimately to be collected in a chamber 38 from which the air is exhausted through ducts 40.

Preferably I close the rear of the hood with sliding doors 42 which may be opened manually to permit access to the web and to the parts of the dryer section from the rear of the dryer. I provide the front of my hood with a plurality of doors 44 adapted to be moved upwardly to permit access tothe interior of the dryer section through the front of the hood. In order to open the doors 44 automatically, I may connect chains 46 carried by pulleys 48 to the doors. A motor 50 drives the input shaft of a gearbox 52 to drive line shaft 54 which carries pulleys 48 to raise the doors when access to the interior of the hood is desired.

From the drawings and from the structure thus far described, it will be apparent that there exists a space 56 between the rear frame 22 and wall 36 and doors 42. Another space 58 exists between the front frame 20 and front wall 34 and doors 44. As has been explained hereinabove, in most modern installations, space 56 is in a large part occupied by pipes (not shown) for supplying steam to the dryer rolls 12 and 14, as well as with gearing associated with the dryer and felt rolls. Owing to the fact that this structure per se forms no part of my invention, it is not shown in the drawings and will not be described in detail. However, as has further been pointed out, owing to the presence of this structure, in the space 56 air supplied by the distributor 30 tends to migrate transversely of the dryer section as it moves upwardly therethrough, or from left to right in FIGURE 1, toward the relatively open space 58. For that reason, as well as because of the structure of roof 32 and the outlet chamber 38, scavenging air supplied by the distributor 30 is not exhausted evenly from front to back of the dryer section and consequently, particularly in the case of installations for producing wide sheets, the web is not dried evenly across its width.

My flow control system for the dryer section includes a rear plenum chamber wall 60 which extends from a point slightly below the peak 62 in roof 32 to a point spaced slightly from rear wall 36 just below the opening into the chamber 38. In the form of my system shown in FIGURES 1 and 2, I provide a plenum chamber front wall 64 which extends from the top of the front frame 20 to a point spaced from the upper end of the wall 60. Both the walls 60 and 64 extend throughout the length of the dryer section 10. It is to be noted that the upper ends of both walls terminate adjacent the centerline of the section.

I provide the dryer with a rear curtain or baffle 66 pivotally supported on a hinge 68 on wall 60 for movement between the full-line position in FIGURE 1 wherein it is retained by a latch 70 to the broken-line position shown in FIGURE 1. In the full-line position which, as will be described hereinafter, is the operative position of the curtain 66, it extends to a point spaced somewhat above the vapor pocket of the dryer. In one particular installation, for example, that point may be about four feet above the pocket where the hood peak 62 is about 29 feet above floor 28. My system includes a front curtain or bafile 72 pivotally supported on a hinge 74 on frame for movement between the full-line position shown in FIGURE 1 and the broken-line position shown in the figure. As will be explained in more detail hereinafter, pitch chains 76 secured to the front curtain '72 ride around idlers 78 and are actuated by pulleys 80 on shaft 54 to permit the front curtain 72 to be moved to the broken-line position concomitantly with elevation of doors 44 to permit access to the parts of the dryer section. In its full-line position, curtain 72 extends from the roof 32 downwardly to a point corresponding generally to that to which the rear curtain 66 extends.

From the structure thus far described, it will readily be apparent that the walls 60 and 64, together with the curtains 66 and 72, form a plenum chamber indicated generally by the reference character 82 adjacent the top of the section.

Edges of the rear wall 60 and front wall 64 adjacent the peak 62 form an elongated narrow opening 84 through which moisture-laden air can escape to the exhaust chamber 38. I provide the opening 84 with an adjustable damper 86 pivotally supported on the wall 64 and adapted to be manually positioned in any suitable manner known to the art to regulate the flow of air out through the opening. Other air coming from the lower part of the space 58 adjacent the front of the dryer may flow upwardly through the narrow space between the top wall 32 of the hood and the plenum wall 64. Air travelling upwardly through the space between the rear frame 22 and rear wall 36 normally is permitted to flow to the exhaust through the opening between the rear edge of the rear plenum wall 60 and the rear wall 36 to the hood. Preferably I provide a second manually positionable damper 88 for controlling the flow of drying air through that space. I have discovered that the arrangement of the plenum chamber just described inhibits the migration of drying air from back to front of the dryer as it moves upwardly through the section. It provides a plenum chamber adjacent the top of the dryer which assures more even distribution of air fiow upwardly, thus more effectively to dry the paper web. It ensures that there are no areas of appreciably unequal drying across the width of the web. Dampers 86 and 88 may be positioned to achieve minor regulations of air flow.

When, for any reason, access to the interior of the dryer from the front is desired, motor 50 is energized to drive shaft 54 to lift the doors 44 through the medium of the chains 46. At the same time chains 76 move the curtain 72 to the broken-line position to alford access to the upper parts of the dryer. If access to the rear of the machine is to be had, doors 42 may be opened and latches 70 can be released to permit the rear curtain 66 to be moved manually to the broken-line position shown in the drawing for access to the upper parts of the dryer from the rear.

Referring to FIGURE 3, I have shown an alternate and somewhat simpler form of my air fiow control system in which the sloping front portion of the hood top or roof forms a front plenum chamber wall similar to the wall 64. The rear plenum chamber wall 90 in this form of my system extends from the rear wall 36 of the dryer to a point below peak 62 to form the elongated narrow opening 92 through which moisture-laden air from the dryer section must pass to reach the exhaust chamber 38.

I provide the form of my system shown in FIGURE 3 with a rear baffie 94 carried by a hinge 96 on the rear wall 36. In the operative position of curtain 94, it rests on an adjustable stop 98 carried by a flange 100 on frame 22. The opening between the flange 100 and the curtain 94 permits a slight flow of air toward the top of the dryer. A hinge 102 adjacent the dryer front wall 34 pivotally supports a front curtain 104 for movement between a position at which it rests on an adjustable stop 98 and a position shown in broken lines in the figure. Chains 76 are connected to the curtain 104 to permit it to be raised to the broken line position when access to the interior of the machine is desired.

In the operating position of the parts of the form of my system shown in FIGURE 1, the doors 44 are lowered and doors 42 are closed The front curtain 72 is in the full-line position shown wherein it is generally parallel to the front wall 34 of the dryer. The rear curtain 66 is held by latch 70 in the full-line position. Air is supplied to the dryer through the distributor 30 adjacent the bottom of the section As has been pointed out hereinabove, the air supplied by distributor 30* flows upwardly through the dryer section and ultimately is exhausted from the chamber 38. The arrangement of my system provides a narrow opening between rear wall 36 and the rear edge of the plenum chamber wall 60 for the flow of air. The sloping front part of the dryer top 32 and the plenum chamber front wall 64 form a second opening through which air can pass to the exhaust. Walls 60 and 64 together with the curtains 66 and 72 provide a plenum chamber 82 at the top of the dryer section wherein air passing upwardly is collected. This air from the chamber 82 may flow through the opening 84 to the exhaust chamber 38. The pivoted dampers 86 and 88 are adjusted for the desired flow conditions. This arrangement ensures even flow of the drying air upwardly through the dryer to prevent unequal drying across the width of the web. In achieving this result, the arrangement inhibits the tendency of the air supplied to migrate from back to front of the dryer as it moves upwardly therethrough.

The form of my system shown in FIGURE 3 is generally similar to that shown in FIGURE 1. The two bafiles 94 and 104 act as dampers to adjust the volume flow of air upwardly through the front and rear spaces between the frame and the hood walls. In this form of my invention all of the air supplied is forced to flow through the narrow opening 92 in order to reach the exhaust.

When access is to be had to the interior of the dryer, motor 50 is energized to drive the line shaft 54 concomitantly to raise doors 44 and to lift either curtain 72 or baflle 104 to a broken-line position. It will readily be appreciated that access to the machine in most instances is to be had through the front. In the event that it becomes necessary to gain access to the machine from the rear, either curtain 66 or baflle 94 is manually moved to the broken-line position.

It will be seen that I have accomplished the objects of my invention. I have provided an airflow control system for a paper machine dryer which ensures even drying across the width of the web. My arrangement reduces the stack effect at the front of the hood. It inhibits migration of drying air from back to front of the machine as the air travels upwardly therethrough, I so arrange my control system as to permit ready access to the interior of the dryer when desired.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. An air flow control system for a paper machine dryer section having longitudinally extending front and rear frames for supporting drying cylinders in a drying space above a mill floor and provided with a hood sup plied with drying air from below said floor, said hood disposed over said frames and having a roof and respective front and rear walls spaced from the front and rear dryer frames, said hood having an exhaust for moisture laden air adjacent the top of said section and extending outwardly of one of said hood walls, including means comprising an inclined wall extending from a location closely adjacent said one hood wall in front of said exhaust to a location adjacent the hood roof near the longitudinal centerline thereof forming a plenum chamber within the hood adjacent the top of the dryer section, said plenum chamber having a narrow opening formed in part by an edge of said inclined wall adjacent said roof, said opening connecting said chamber to said exhaust, and means located above said floor and within said hood for inhibiting migration of air transversely of said drying space in order to direct drying air upwardly through said drying space toward said plenum chamber, said inhibiting means comprising means for reducing air flow upwardly through the space between said front frame and said hood wall.

2. A system as in claim 1 in which said hood has a roof and in which said inhibiting means comprises a front plenum chamber wall, means mounting said front chamber wall in closely spaced relationship to said dryer roof and a vertically extending curtain on said front frame.

3. A system as in claim 1 in which said hood has a roof and in which said inhibiting means comprises a front plenum chamber wall, means mounting said front chamber wall in closely spaced relationship to said dryer roof, a vertically extending curtain, means mounting said curtain on said frame for pivotal movement away from the frame to permit access to said 'dryer and means adapted to be energized to pivot said curtain.

4. A system as in claim 1 wherein said inhibiting means comprises a baflle extending transversely of the space between the hood front wall and the dryer front frame.

5. A system as in claim 1 in which said inhibiting means comprises a batlle extending transversely of the space between the hood front wall and the dryer front frame, means mounting said baflie for pivotal movement out of said space and means adapted to be energized to pivot said bafile.

6. A system as in claim 1 in which said inhibiting means comprises a curtain extending transversely of the space between the rear hood wall and the rear dryer frame.

7. A system as in claim 1 in which said inhibiting means comprises a curtain extending transversely of the space between the rear hood wall and the rear dryer frame and means mounting said curtain for pivotal movement out of said space.

8. A system as in claim 1 in which said dryer is provided with rolls adapted with said cylinders to form a pocket region and in which said inhibiting means are located out of said pocket region.

9. In a paper machine dryer having front and rear longitudinally extending frames and a hood with a roof and front and rear walls spaced from said frames, means for supplying said dryer with drying air from below, means for exhausting moisture laden air from said hood adjacent its top at one side of the longitudinal centerline of the dryer, an air flow control system including a plenum chamber comprising a rear plenum chamber wall sloping downwardly and rearwardly from adjacent the top of said hood adjacent said centerline to a location closely spaced from said hood rear wall, a front plenum chamber wall sloping downwardly and forwardly from adjacent the top of said hood toward said front dryer frame in closely spaced relationship to said hood roof, said front and rear plenum walls cooperating to form a narrow opening adjacent said centerline communicating with said exhausting means, a front curtain carried by said front frame for directing air travelling upwardly through the space between said front frame and said hood front wall into the space between the front plenum wall and the hood roof, a rear curtain, and means positioning said rear curtain to direct air travelling upwardly through the space between said rear frame and said hood rear wall to the space between said rear plenum chamber wall and the rear hood wall.

10. A system as in claim 9 including a first positionable baflle for regulating flow through said narrow opening and a second positionable bafile for regulating the flow through the space between said rear plenum wall and the hood rear wall.

11. A paper machine dryer as in claim 9 in which said hood includes normally closed access doors and energizable means for opening said doors, said air control system including means mounting said front curtain on said front dryer frame for movement away from said frame and means responsive to said energizable means for pivoting said curtain.

12. In a paper machine dryer having front and rear longitudinally extending frames for supporting drying cylinders in a drying space above a mill floor and provided with a hood with a roof having front and rear walls spaced from said frames, means for supplying drying air to said drying space from below said floor, means for exhausting moisture laden air from said hood at one side thereof, an air flow control system including a plenum chamber comprising a rear plenum chamber wall sloping downwardlly and rearwardly from adjacent the top of the hood to said hood rear wall and a portion of said hood roof sloping downwardly and forwardly from adjacent the top of the hood to said hood front wall, said rear plenum wall and said dryer roof portion cooperating to form a narrow opening adjacent the top of said hood and providing communication with said exhausting means, a front curtain extending transversely of the space between said hood front wall and said dryer front frame adjacent the upper region of said drying space and a rear curtain extending transversely of the space between the hood rear wall and the dryer rear frame adjacent the upper region of said drying space for directing drying air into said plenum chamber.

References Cited UNITED STATES PATENTS 2,000,546 5/1935 Woodsome 34ll4 XR 3,143,397 8/1964 Keefe 34-174 1,285,615 11/1918 Canepa et al 34229 XR 1,890,568 12/1932 Bleibler 341 14 2,909,847 10/1959 Hornbostel 34114 XR 2,910,784 11/1959 Metcalfe 34-116 XR 2,977,686 4/1961 Stout 34114 JAMES W. WESTHAVER, Primary Examiner.

H. B. RAMEY, Assistant Examiner. 

